AD9925BBCZ datasheet(57/96 Pages) AD

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AD9925

Rev. A | Page 57 of 96

the individual supply pins are separately bypassed. A separate

e care-

lly decoupled to ground as close as possible to their respective

pins. The analog input (CCDIN) capacitor should also be located

close to the pin.

CIRCUIT LAYOUT INFORMATION

The AD9925 typical circuit connections are shown in Figure 73.

The PCB layout is critical in achieving good image quality from

the AD9925. All of the supply pins, particularly the AVDD,

TCVDD, RGVDD, and HVDD supplies, must be decoupled to

ground with good quality, high frequency chip capacitors. The

decoupling capacitors should be located as close as possible to

the supply pins and should have a very low impedance path to a

continuous ground plane. There should also be a 4.7 µF or larger

value bypass capacitor near each main supply—AVDD, HVDD,

DRVDD, VL, and VH—although this is not necessary for each

individual pin. In most applications, it is easier to share the

supply for RGVDD and HVDD, which may be done as long as

3 V supply may also be used for DRVDD, but this supply pin

should still be decoupled to the same ground plane as the rest

the chip. A separate ground for DRVSS is not recommended.

The analog bypass pins (REFT and REFB) should also b

The H1 to H4 and RG traces should be designed to have low

inductance to avoid excessive distortion of the signals. Heavier

traces are recommended because of the large transient current

demand on H1 to H4 by the CCD. If possible, physically locat-

ing the AD9925 closer to the CCD will reduce the inductance

on these lines. As always, the routing path should be as direct as

possible from the AD9925 to the CCD.

The AD9925 also contains an on-chip oscillator for driving an

external crystal. Figure 72 shows an example of an application

using a typical 24 MHz crystal. For the exact values of the exter-

nal resistors and capacitors, it is best to consult with the crystal

manufacturer’s data sheet.

20pF

CLI

CLO

AD9925

24MHz

XTAL

Ω

500

Ω

Figure 72. Crystal Driver Application

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